(1) Field of the Invention
The present invention relates to a gel-coated seed.
(2) Description of the Related Art
The gel-coated seed technology (i.e., technology of coating seeds with gel) improves a conventional labor-intensive agriculture including excessive sowing in the field taking low gemmation rate of seeds into consideration, that is, taking the fact that the bud barely or hardly comes out from the coating gel-layer after the gel-coated seed germinates, and thinning out after gemmation.
The technology is an epoch-making technology, by which a seedling can securely be obtained from a grain of seed with the aid of water or other constituent contained in a coating gel-layer and furthermore a crop can be obtained. The technology enables the use of F1 seeds, which is excellent and very expensive, thereby attaining significant improvement in yield and quality. The technology is really good news for Japanese agriculture, which should survive in the condition that high quality and cheap vegetables and flowers are imported from neighboring Asian countries.
At the beginning, the coating gel-layer of the gel-coated seed was composed of only alginic acid-based aqueous gel. However, since the alginic acid-based aqueous gel is relatively hard, such a gel-coated seed had a problem in terms of “standing-up of seedling” (explained below). In other words, since the alginic acid-based aqueous gel is relatively hard, the bud of a coated plant may become difficult to grow or may not come out from the coating gel-layer to die. Consequently, such a measure has been employed that grains consisting of hydrophilic polymer and water are distributed in the coating gel-layer.
In this specification, the “standing-up of seedling” is defined as a condition that a gel-coated seed sown in a field germinates, the bud comes out from the coating gel-layer and further comes out from the soil of the field, and it becomes a defect-free plant body with the first leaf thereof being completely out (i.e., being completely extends). A ratio (%) of seeds, each of which has a good property in terms of “standing-up of seedling” described above, relatively to all seeds sown is called “ratio of standing-up of seedling” in this specification.
The gel-coated seed, in which grains consisting of water-containing hydrophilic polymer are distributed in the coating gel-layer consisting of alginic acid-based aqueous gel, is produced, for example, by the following manner.
A weighing is carried out so that the concentration of sodium alginate becomes 0.9 wt % and the final concentration of powdered starch polyacrylate-based hydrophilic polymer (i.e., starch-acrylic acid graft polymer) becomes 0.2 wt %, then water is added thereto so as to dissolve the sodium alginate sufficiently. At that time, the hydrophilic polymer absorbs water to be granular and is dispersed by stirring. By using this liquid dispersion (i.e., gel-forming liquid in which the grains consisting of the water-containing hydrophilic polymer are dispersed), a droplet thereof is formed at a lower end of a hollow tube, into which a seed is introduced from the interior of the hollow tube, and then the resultant droplet is dropped in a solution containing multivalent metal ion having concentration of 12-14 wt % such as an aqueous solution (hardening liquid) of calcium chloride, thereby obtaining a gel-coated seed including a coating gel-layer, which is insolubilized against water.
Since the strength of thus produced coating gel-layer is very strong, in order to attain a better property in terms of standing-up of seedling, a gel-coated seed having low concentration of alginate has been produced, by which a three-dimensional network structure obstructing the growth of the seed due to the alginic acid in the coating gel-layer is weakened.
In such a case, however, since the strength of the coating gel-layer is deteriorated, when a hopper is used upon handling of the gel-coated seeds such as mechanical sowing, the gel-coated seed is crushed and deformed causing the hopper stuck and otherwise the surface layer of the gel-coated seed comes off causing the mechanical sowing unable to be carried out, that is, handling property thereof is deteriorated and the originally intended effect for the gel-coated seed cannot be attained.
Therefore, in order to attain sufficient strength of the coating gel-layer in such a condition that the using amount of the alginate is reduced, the amount of the hydrophilic polymer is significantly increased.
By this measure, the coating gel-layer having sufficient strength in usual use is obtained. However, when the coating gel-layer is dried for the purpose of storing the gel-coated seed and thereafter the coating gel-layer is provided with water for sowing the gel-coated seed, the coating gel-layer is not sufficiently recovered, that is, the coating gel-layer becomes spongy deteriorating its strength significantly and the gel-coated seed thus obtained becomes hard to be handled.